1. Field of the Invention
This invention relates to a method of examining the extent and distribution of surface defects including crystal defects and contamination with impurities of silicon wafers, which occur in the process of manufacturing semiconductor silicon wafers and in the process of fabricating silicon devices by processing the semiconductor silicon wafers.
2. Description of the Prior Art
In the process of fabricating silicon devices, it is well known that deterioration occur when crystal defects are present in the device active areas of silicon wafers.
In the process of fabricating silicon devices, it is well known that, when silicon wafers are heat-treated, harmful impurity metal elements are attracted to crystal defects to precipitate thereto. As a technique utilizing such phenomenon, gettering is known in the art, according to which crystal defects are formed intentionally in the area other than the device active area in a silicon wafer surface and impurity metal elements are collected thereto. However, if crystal defects are present in the silicon wafer surface, the impurity metal elements precipitate to the crystal defects and are trapped to make resulting devices deteriorative. The extent to which the impurity metal elements are trapped by such crystal defects differs depending on the type or state of crystal defects or the type of impurity metal elements. Usually, the impurity metal elements that may be trapped in crystal defects and are harmful in the process of fabricating silicon devices in semiconductor factories are typified by heavy metals such as Cu, Fe and Ni, and alkali metals and alkaline earth metals such as Na and Ca. Hence, such impurity metal elements are main targets for making clean the silicon device fabrication process.
Hence, the examination of crystal defects in silicon wafer surfaces is an important item in surface evaluation of semiconductors. As typical examination methods, there is, e.g., a method in which, utilizing the tendency that etching reaction locally takes place at crystal defects in the surfaces, the crystal defects in silicon wafers are actualized by selective etching so that the defects can be observed by a microscope. It is also common to use an electron microscope to directly observe the areas having crystal defects in the surface. As a method of directly observing disorders of crystal lattices, there is a method in which X-ray diffraction is utilized, such as X-ray lang's method. It is also attempted to use a method in which light is projected on silicon wafer surfaces and its reflectance or complex refractive index spectra are measured to examine the crystal defects in the surfaces.
Most of these examination methods, however, are suited for the examination of crystal defects microscopically or locally present in the silicon wafer surfaces, and many of them are not suitable for catching the whole distribution of crystal defects in silicon wafer surfaces. For example, in the above examination method making use of etching, the distribution of crystal defects in the whole silicon wafer surface can not be observed with the naked eye except the case when any lineage, strong structural defects, appear to the silicon wafer surfaces or when a large quantity of dislocation or micro-defects appear in a haze. Also, the X-ray lang's method using X-ray diffraction is suited for the examination of structural defects such as dislocation and layer defects and enables photographic observation of the distribution of such structural defects of the whole silicon wafer surface, but is not effective as an examination method for amorphously damaged or cluster of point defects like the defects caused by ion implantation.
Furthermore, the examination methods described above can not examine contamination with impurities which can absorb on areas having no crystal defects and may form surface states.